A reliable, compact, and repetitive-rate high power microwave generation system.

The relativistic magnetron with diffraction output (MDO) is promising to be the most compact narrow band high power microwave source. In this paper, based on the theory of S-parameters, a method named “choosing optimum” is proposed for the efficient design of the MDO in any wave band. By means of S-parameters, the π-TE31 mode conversion efficiencies of an S band MDO are calculated and then verified by three-dimensional particle-in-cell simulations. In order to illustrate the advantage of the choosing optimum method, the S-parameters of another L-band MDO are computed in a wide range of structure parameters and two results are chosen with detail information. Compared with the conventional method, the choosing optimum method is not only a shortcut, but also a convenient and easy way for choosing the high efficient MDOs in any wave band to meet the needs of different applications.

Investigation of material migration and characterization of the film layer on the surfaces of HPM generator structures

The relativistic magnetron with axial extraction, also known as magnetron with diffraction output (MDO), is an important device for the miniaturization and compaetification of magnetron. It is also promising to be one of the most compact narrow band high power microwave sources. Based on the manners and traits of the MDO directly radiating the quasi-TE11 mode in axial direction, the investigation of the power combination of double MDOs with a horn antenna is carried out. After discussing the combination ways and results, a modified configuration is proposed for improving the radiation directivity. Finally, the results show that when the adjacent double MDOs have an open angle of 7 and the common horn antenna has the parameters of h = 600 mm and r = 340 mm, the mode reflection coefficient of the power combination system is 0.31, the maximum gain is 21.5 dB, the radiation mode is TE11.

Experimental operation of a high power microwave source with a metamaterial (MTM) structure is reported at power levels to 2.9 MW at 2.4 GHz in full 1 μs pulses. The MTM structure is formed by a waveguide that is below cutoff for TM modes. The waveguide is loaded by two axial copper plates machined with complementary split ring resonators, allowing two backward wave modes to propagate in the S-Band. A pulsed electron beam of up to 490 kV, 84 A travels down the center of the waveguide, midway between the plates. The electron beam is generated by a Pierce gun and is focused by a lens into a solenoidal magnetic field. The MTM plates are mechanically identical but are placed in the waveguide with reverse symmetry. Theory indicates that both Cherenkov and Cherenkov-cyclotron beam-wave interactions can occur. High power microwave generation was studied by varying the operating parameters over a wide range, including the electron beam voltage, the lens magnetic field, and the solenoidal field. Frequency tuning with a magnetic field and beam voltage was studied to discriminate between operation in the Cherenkov mode and the Cherenkov-cyclotron mode. Both modes were observed, but pulses above 1 MW of output power were only seen in the Cherenkov-cyclotron mode. A pair of steering coils was installed prior to the interaction space to initiate the cyclotron motion of the electron beam and thus encourage the Cherenkov-cyclotron high power mode. This successfully increased the output power from 2.5 MW to 2.9 MW (450 kV, 74 A, 9% efficiency).

Summary form only given, as follows. To broaden our knowledge in radio frequency (RF) and a high power microwave (HPM) generation, it is useful to energize our advanced RF& HPM source with a driver that has low internal impedance. It is useful to find out if our source also suffers from limitation known as shortening. This means that by increasing the radiative power, the length of the pulse becomes shorter. Hence, there is a limitation in the energy radiated in a single shot. This paper describes a compact six stage-Marx generator. It is built using the concept of pulsed-forming networks. The capacitance per stage is 0.500 F and the charging voltage is organized to vary from 25 to 100 kV. With the matching (dummy) load of 7.5 ohms; used, the maximum output voltage should be 300 kV and the maximum output current 40 kA. The stored energy in the system is 15 kJ and the peak power supplied to the load of 7.5 Ohms is 12 GW. Without crowbaring, the pulse width is 0.82 ns. When the crowbar switch is added, the pulse width can vary from 100 to 500 ns in a predictable manner.

The aim of this work is to design a novel metamaterial slow wave structure (SWS) for high power microwave (HPM) generation using a short pulse relativistic electron beam. The structure provides around 15% efficiency with 250 MW output power at 1.4 GHz frequency. It generates backward wave generation and beam-wave interaction with a TE 21 -like mode.

6H-SiC photoconductive semiconductor switches (PCSS) are new alternative of high power microwave (HPM) or RF generators with the special potential of compactness, tunable frequency and pulse width due to the superior material properties. For PCSS behavior investigation including on-resistance and transient, optical absorption, carrier process, and circuit elements are commonly important issues. This brief builds the major physics framework from the expressions of these influence factors considering simplicity and reliability. According to the basic physics models, a scalable, general model of vanadium compensated, semi-insulating (VCSI), vertical 6H-SiC PCSS is constructed in PSpice. The experiments are performed to verify this circuit model. Consequently, the correspondence between the measured results and simulation results proves its applicability.

A compact 180 kV electron beam system is designed for high power microwave generation. The electron beam system is consists of a secondary energy storage device, which can deliver energy to the load at faster rate than usual primary energy storage system such as tesla transformers or marx generator. The short duration, high voltage pulse with fast rise time and good flattop is applied to vacuum diode for high power microwave generation. The compact electron beam system is made up of single turn primary tesla transformer which charges a helical pulse forming line and transfers its energy to vacuum diode through a high voltage pressurized spark gap switch. We have used helical pulse forming line which has higher inductance as compared to coaxial pulse forming line, which in turns increases, the pulse width and reduce the length of the pulse forming line. Water dielectric medium is used because of its high dielectric constant, high dielectric strength and efficient energy storage capability. The time dependent breakdown property and high relative permittivity of water makes it an ideal choice for this system. The high voltage flat-top pulse of 90 kV, 260 ns is measured across the matched load. In this article we have reported the design details, simulation and initial experimental results of 180 kV pulsed electron beam system for high power microwave generation.

Summary form only given. This paper describes the numerical study and experimental results of an axial vircator with axial extraction. The microwave source is driven by a Marx generator and excludes any type of pulse forming device between the two subsystems. The main reason for this special arrangement is the final goal to build a compact and robust high power microwave system. The drawback is usually a lower efficiency of the microwave source. The vircator operates with the applied voltages between 200 and 400 kV and the impedance is around 50 Ohms during the process when microwave radiation is generated. The microwave pulse duration is for most cases between 50 to 100 ns. For the experiments described in this paper focus has been on different cathode geometries. Results that are given include microwave power, spectral content and mode characteristics. In an attempt to better understand and explain the experimental results particle-in-cell simulations have been carried out in MAGIC. These numerical results support to some extent the experimental results.

The past decade has seen significant advances in the science and technology of high power microwave (HPM) sources (MW-GW) driven by pulsed-power/ high current electron beams. The applications of these high power microwave sources have expanded to defensive measures, including homeland security and countermeasures against improvised explosive devices. In particular, major strides have been made in relativistic magnetrons, with the recirculating planar magnetron (RPM) [1–4], transparent cathodes [5], mode-control cathodes for phase-locking [4], and other innovations. The RPM consists of two, linear, cavity-arrays coupled by recirculating sections. The central-cathode structure supplies much higher current than conventional, cylindrical magnetrons. Recent results from UM's RPM-12a, a 1-GHz, double-coaxial extractor prototype, have demonstrated extracted microwave powers of 140 MW at peak efficiencies of 40%. A 6-extractor design with goals of 400 MW, at 50–60% efficiency is under construction. Simulations show promising results for a multi-frequency RPM in which two, planar slow-wave structures are employed with different resonant frequencies. There have also been important developments in plasma-based techniques for mitigating the effects of HPM pulses on electronic components. Impressive results have been achieved by a consortium of universities in the rapid-cutoff of microwave pulses by plasma-limiters. This presentation will summarize the recent scientific advancements in both HPM source development, as well as techniques to rapidly absorb or reflect these microwave pulses.

A compact and modular pulse forming network (PFN)-Marx generator with output parameters of 5 GW, 500 kV, and 30 Hz repetition is designed and constructed to produce intense electron beams for the purpose of high-power microwave (HPM) generation in the paper. The PFN-Marx is composed by 22 stages of PFN modules, and each module is formed by three mica capacitors (6 nF/50 kV) connected in parallel. Benefiting from the utilization of mica capacitors with high energy density and a mini-trigger source integrated into the magnetic transformer and the magnetic switch, the compactness of the PFN-Marx system is improved significantly. The structure of the PFN module, the gas switch unit, and the connection between PFN modules and switches are well designed for modular realization. Experimental results show that this generator can deliver electrical pulses with the pulse width of 100 ns and amplitude of 500 kV on a 59-ohm water load at a repetition rate of 30 Hz in burst mode. The PFN-Marx generator is fitted into a cuboid stainless steel case with the length of 80 cm. The ratio of storage energy to volume and the ratio of power to weight of the PFN-Marx generator are calculated to be 6.5 J/L and 90 MW/kg, respectively. Furthermore, utilizing the generator to drive the transit time oscillator (TTO) at a voltage level of 450 kV, a 100 MW microwave pulse with the pulse width of 20 ns is generated.

In this paper, a high power relativistic backward wave oscillator (BWO) experiment is reported. A 230 kV, 2 kA, and 150 ns relativistic electron beam source is developed using a Marx generator. The beam is then injected into a hollow rippled wall metallic cylindrical tube that forms a slow wave structure (SWS). A BWO is a slow wave structure in the form of a rippled wall wave-guide and is used as a source of high power microwave generation when excited by a relativistic electron beam (REB). The beam is guided using an axial pulsed magnetic field having, the duration 1 ms and strength being 1.0 Tesla, respectively. This field is generated by discharge of a capacitor bank into a solenoidal coil. A synchronization circuit ensures the generation of the electron beam at the instant when the axial magnetic field attains its peak value. The electron beam interacts with the SWS waveguide modes and generates microwaves due to Cherenkov interaction. Estimated power of ~2 MW in TM01 mode is observed.

Monte Carlo simulation of THz frequency power generation in notched n +–n −–n–n + 4H-SiC structures

An axially extracted virtual cathode oscillator has been fabricated. This ultra-high-power microwave generator is powered by the Chundoong intense relativistic electron beam pulser (Max: 600 kV, 88 kA, and 60 ns duration). In this experiment, a solid electron beam with a peak diode current of 21 kA is obtained from the pulser operated at a peak diode voltage of 300 kV. It is found in this experiment that the peak of microwave emission occurred at the moment of the second peak in electron beam current, where the diode voltage V/sub d/ and diode current I/sub d/ are V/sub d/=290 kV and I/sub d/=21 kA, respectively. This observation might be strongly correlated to the inherent oscillations of the electron cloud in time and space originated from both the dynamics of the reflected electron beam due to virtual cathode and oscillations of the virtual cathode itself, from which the peak of high-power microwave can be generated in this experiment. The major operating output frequencies have been measured to be 6.68 GHz/spl les/f/spl les/7.19 GHz based on the waveguide dispersive delayed line method, which is in good agreement with that from MAGIC computational results for an electron beam voltage of 290 kV and a diode current of 21 kA. The maximum microwave output power from the virtual cathode oscillator has been measured to be 200 MW in this experiment. while its power conversion efficiency is approximately 3.3%. The dominant emission mode from the virtual cathode oscillator is shown to be the TM/sub 01/ mode based on the emission pattern of microwave induced air breakdown in this experiment.

The diagnostics used to measure the voltage and current of the vacuum diode used in the high power microwave generator at Texas Tech University are discussed. The current probe is a transmission line Rogowski coil that has demonstrated nanosecond risetinies and has an output proportional to the excitation current for approximately 70 nanoseconds. The voltage probe is a software compensated resistive divider.